Photo-sensitive devices are used in a variety of electronic devices. For example, an array of photo-sensitive devices can be used to form an image sensor array to be used in a digital camera. A photo-sensitive device typically includes an active region within a semiconductor material that transfers energy from photons into electrical energy.
Each cell within a photo-sensitive device array includes the main photo-sensitive device as well as some circuit components such as transistors and resistors that are used to measure the electric current produced by the photo-sensitive device. It is important that these circuit components are isolated from the photo-sensitive region because stray electric current can cause dark currents within the photo-sensitive region. This adversely affects the light intensity measurements performed by the photo-sensitive region.
One way to isolate the device structures is to use shallow trench isolation. Shallow trench isolation is a common technique used in semiconductor fabrication and involves the formation of a shallow trench that is then filled with a dielectric material. This technique, however, involves plasma etching which can damage the surface of the substrate. This can adversely affect the performance of the photo-sensitive array.
Another method of isolation is a technique referred to as device isolation. This technique involves the formation of a doped semiconductor material instead of a dielectric material. The doped semiconductor material is of a different concentration than the doping concentration of adjacent semiconductor materials, thus forming a junction. However, this technique is less effective when isolating source/drain regions from photo-sensitive devices. Thus, it is desirable to find a method of isolation that effectively protects the photo-sensitive devices without causing damage to the surface of the substrate.